This invention relates to a control signal generator for generating a control signal to be used for tracking control or the like at the time of playback on a video tape recorder or the like, and to a signal separator for separating a reference signal for editing of video signals from the control signal.
Generally in the video tape recorder, it is necessary for the reproduce head to precisely trace the video signal recorded tracks upon playback. This is called tracking. In order to perform tracking, a signal indicating the rotational position of the record head for recording the video signal (hereinafter, referred to as the control signal) is recorded along the longitudinal direction of the video tape, and upon playback this control signal is reproduced so that the position in which the video signal is recorded is detected. Then, control is made to minimize the difference between the phase of the control signal and the phase of the reproduce head for reproducing the video signal, thereby achieving tracking. So far, the frame signal (the rectangular wave signal corresponding to one picture of the video signal) separated from the video signal has been recorded as the control signal on the video tape.
Moreover, on the video tape recorder, a new video signal is recorded to be continuous to the end of the previously recorded video signal on the video tape or to be inserted mid way of the previously recorded video signal on the video tape. This operation is called editing. In this case, upon recording the previously recorded old video signal is just connected to the recorded new video signal in synchronism therewith so that upon playback the reproduced picture is not disturbed at the junction. It is the general practice that for the synchronization between the old and new video signals the frame signal separated from the recorded new video signal is synchronized with the control signal corresponding to the frame of the previously recorded old video signal. As another method of synchronization, the subcarrier signal of the color signal is also synchronized therewith in addition to the frame synchronization. The video signal includes the subcarrier signal for the transmission of the color signal. This subcarrier signal is not returned to the original phase within one frame period. The period in which it is returned to the original phase is two frames in the NTSC system video signal, or four frames in the PAL system video signal. This period is called the color frame period. The group of frames in the color frame period is called the color frames. The first frame of the color frames is specified by the horizontal synchronization signal at a predetermined position and the phase of the subcarrier. The above-mentioned control signal is difficult to be synchronized with the color frames because the phase of the color frames of the recorded video signal is unknown. Therefore, the duty ratio of the control signal is changed with the color frame period so that the color frame information can be carried on the control signal (see "High Performance M II VTRAU660" written by Atushi Kuninaga and others, National Technical Report Vol. 34, No. 6, Dec. 1988, p 89-96 or "M II 625/50 (PAL) format VTR" written by Seiichi Hashimoto and others, National Technical Report Vol. 34, No. 6, Dec. 1988, p. 97-103). Then, the color frame signal (the signal corresponding to one color frame of the video signal) separated from the recorded new video signal is synchronized with the color frame signal separated from the reproduced control signal, thereby easily achieving the color frame synchronization.
In recent years, as the video tape recorder has been digitalized for high performance, the video signal recorded tracks have become narrower and thus more stable tracking has been desired. To satisfy this demand, it is considered that the control signal constituting the reference signal for the tracking is recorded at a higher frequency than the frame signal. However, if the control signal is merely recorded at a higher frequency than the frame signal for the purpose of stabilizing the tracking, the control signal and the frame signal cannot be easily synchronized upon editing. Thus, in order to increase the frequency of the control signal and make synchronization with the control signal upon editing, the control signal, a signal as a reference for the tape travel and a reference signal for editing, or information of frame and color frame signals are simultaneously recorded, and upon playback, the reference signal for the tape travel and the reference signals for the editing are separated and used for the above purposes (the reference for the tape travel and the editing).
For such a video tape recorder, the International Radio Communications advisory committee standardized a DI format video tape recorder for a broadcasting digital video tape recorder in 1986. In the DI format video tape recorder, when an NTSC system video signal is recorded, the video signal of each frame is divided into parts of 20 tracks. Then, one pulse for each four tracks is recorded as a reference point for the tape travel. Thus, five reference points for the tape travel correspond to one frame of the video signal. At the reference point for the tape travel corresponding to the beginning of the frame of the video signal, a pulse indicating the beginning of the video signal is recorded at a position following the pulse indicating the reference point for the tape travel. Since in the NTSC system video signal two frames is one color frame period, at the reference point for the tape travel corresponding to the beginning of the color frame of the video signal a pulse indicating the beginning of the color frame of the video signal is recorded at a predetermined position following the pulse indicating the beginning of the frame of the video signal. These pulse signals are recorded in the longitudinal direction of the video tape by the bias recording system (see "4:2:digital VTR format" written by Takeo Eguchi, the Journal of the Institute of Television Engineers of Japan, Vol. 40, No. 6, 1986, p. 457-464).
The bias recording system, as compared with the saturation recording system used to record the control signal in the conventional analog-type video tape recorder, requires a peaking coil and a bias signal generating circuit, thus having the disadvantage of large circuit scale which leads to high cost and large size. Moreover, since the control signal is generally recorded by the conventional saturation recording system, the conventional control signal recording and reproducing IC cannot be used.
In the conventional saturation recording system, though the color frame information is carried out on the control signal recorded at the frame frequency, there is no provision for increasing the frequency of the control signal and for synchronization with the control signal upon editing by recording the control signal simultaneously with the reference signal for the tape travel and with the reference signals for editing and for upon reproduction, separating and using the reference signal for the tape travel and the reference signals for editing for the above purposes (the reference of the tape travel and the editing).